How to Use an iMac G3 as an External Monitor: Step-by-Step Guide

Need an extra monitor or a larger screen for your Mac? An iMac G3 can serve as an external monitor. This guide will walk you through using an older iMac model as an external monitor, covering both modern and legacy methods:

Method 1: Using AirPlay with macOS Monterey

If you have an iMac G3 with sufficient hardware specifications, you can use it as an external monitor through AirPlay, the wireless protocol provided by Apple.

The iMac acting as an AirPlay receiver must be a model from 2019 or later and running macOS Monterey or later. The Mac sending the AirPlay signal can be any Mac or MacBook from 2011 or later. For mirroring, you’ll need Mountain Lion or later; for extending the screen, you’ll need Mavericks or later. If your older iMac can’t run macOS Monterey or later, you can still use it as a monitor with Target Display Mode.

Steps to Use AirPlay as an External Monitor

Ensure the iMac is capable of receiving AirPlay. Check if it meets the minimum requirements for macOS Monterey. Engage the AirPlay receiver on the iMac: Click the Apple menu. Select Show AirPlay Options. Check the box next to Allow Other People to Use This Mac as an AirPlay Receiver on Your Network. Select who can connect with AirPlay. Pin the Screen Mirroring icon to the menu bar on your sending Mac: Click the Apple menu. Select System Preferences. Check the box next to Screen Mirroring. Select from the drop-down menu. Connect the Macs via Wi-Fi or a USB-C cable. Use a USB-C or Thunderbolt 3 cable for optimal performance, especially for video-intensive tasks. Click the Screen Mirroring icon in the menu bar on the sending Mac. A list of AirPlay 2-compatible devices will appear. Select whether you want to mirror or extend the screen. Choose the iMac from the list to start using it as a monitor. Rearrange your extended display settings if needed: Click the Screen Mirroring icon in the menu bar. Select Display. Drag the displays to reflect their real-life setup. To end the AirPlay session, move the mouse to the top-left corner and click the Stop Sharing slider.

Method 2: Using Target Display Mode on an Older iMac

For iMacs from 2009 to 2014, Target Display Mode is the traditional method to use an iMac as a monitor. It’s not available in the latest macOS versions, but here’s how you can do it:

The iMac acting as a monitor must be a 24 or 27-inch model from 2009 or 2010, or any iMac released between 2011 and mid-2014, running macOS High Sierra or earlier. The Mac connecting to the iMac must be from 2019 or earlier and running macOS Catalina or earlier. Connect the two Macs using a Thunderbolt or Thunderbolt 2 cable (use Mini DisplayPort for iMacs from 2009 or 2010). Log in to a user account on your primary Mac to ensure it can be mirrored. Press Command F2 on the iMac to initiate the Target Display Mode. Make sure you use a keyboard connected to the iMac. While in Target Display Mode, use the primary Mac’s keyboard and mouse to control the iMac. Press Command F2 again to exit Target Display Mode, and the screen will revert to its previous state.

Other Options

Duet Display: Premium software that can turn your iMac into a monitor. Requires a subscription, but a free trial might be available. Luna Display: Another option that improves upon Target Display Mode, allowing any iMac to be used as a second monitor. Requires a special USB-C or Mini DisplayPort dongle and installation of Luna’s software on both systems. Use a TV: Connect your Mac to a TV using a Thunderbolt port, Mini DisplayPort, or HDMI port, and use the TV as a monitor. Even an HDTV with an appropriate port can be used, and you can even play audio from your Mac through the TV. AirPlay to a TV: Use AirPlay 2 to mirror your Mac’s screen to an AirPlay-compatible TV or streaming device, like an Apple TV or Roku, for an extra large screen.

After completing these steps, you can seamlessly integrate your iMac G3 into your existing setup as an external monitor, enhancing your work or entertainment experience.